1. Field of the Invention
The present invention relates to an ink-jet head and an ink-jet recording apparatus using the head and, more particularly, to an ink-jet head in which rows of discharge ports are provided by disposing a plurality of head chips in a direction orthogonal to a direction in which a recording material is carried, and an ink-jet recording apparatus that uses the head.
2. Description of the Related Art
A recording apparatus used with a printer, a copying machine or the like, or as an output unit for compound electronic equipment or a workstation including a computer, a word processor or the like is adapted to record images, including characters and symbols, on a recording material, such as paper or thin plastic sheets, on the basis of recording information.
A full multi-type ink-jet head is available as a recording head used for such recording apparatuses. In the full multi-type recording head, it has been difficult to machine nozzles with no defect over an extensive range, e.g., over a full width of a recording area (unless otherwise specified, the term “nozzle” may be used as a generic term to mean ink discharge ports, liquid passages in communication with the ink discharge ports, and elements disposed in the liquid passages to generate energy used for discharge). If, for example, a printer for outputting photographic toner images on large-sized paper used as materials at offices or the like were to perform recording at 1200 dpi on a sheet of A3-size paper over a recording width of about 280 mm, then about 14,000 discharge ports would be required to cover the recording width. It is extremely difficult to achieve a manufacturing process that makes it possible to machine every nozzle without any defects for such a large number of discharge ports. Even if it were possible to successfully fabricate the nozzles, the nondefective rate would be low, while the manufacturing cost would be extremely high.
As a solution to the problem described above, a full multi-type ink-jet head has been devised. In this type of ink-jet head, a plurality of relatively inexpensive, short chips, which are used in serial type recording apparatuses, is combined and arranged with high accuracy until a desired length is reached. This is called a “spliced head.”
FIG. 17 is a schematic diagram showing a construction example of such an ink-jet head. An ink-jet head IH has two rows of head chips HC numbered in sequence starting with 1 and arranged in a staggered manner. The rows of head chips HC extend in a direction Y in the figure, i.e., the direction orthogonal to or cross the direction in which a recording material is carried. The head chips HC having adjacent numbers are arranged such that they have spliced portions wherein a predetermined number of discharge ports located in end portions overlap each other. Color recording by using the spliced head IH having the configuration described above can be implemented by arranging, in the same chip, the head chips HC that have columns of discharge ports NAC, NAM, NAY, and NABk corresponding to cyan (C), magenta (M), yellow (Y), and black (Bk), respectively, arranged in a direction X in the figure, i.e., the direction in which the recording material is fed, in the staggered manner in a direction orthogonal to or intersectional with the direction in which the recording material is fed.
In every ink-jet head having the construction described above, the spliced portion of each head chip has two discharge ports of all ink colors overlapping at the same location on a line in the recording material feeding direction. Therefore, when an image is formed by discharging the inks onto a recording material, all ink colors overlap in the spliced portion on the line in the recording material feeding direction. As a result, a thickly colored “splicing streak,” which extends in the direction in which a recording material P is fed, frequently shows on a formed image.
To solve the aforementioned problem, an ink-jet head having a construction shown in FIG. 18 has been devised (refer to Japanese Patent Laid-Open No. 2000-289233). In a spliced portion in this ink-jet head, the rows of the discharge ports of color inks are disposed in a staggered manner in the Y direction on the same head chip, and the head chips are arranged such that the discharge ports of the same color ink in adjacent head chips are not positioned on a line in the recording material feeding direction.
However, in the construction illustrated in FIG. 18, a problem arises in some cases in that the absence of overlapping discharge ports of the same color ink on the line in the recording material feeding direction between adjacent head chips produces a “splice streak” or “white streak.” This is represented by, for example, the “deflection at ends” disclosed in Japanese Patent Laid-Open No. 2002-67320. The deflection at ends is a phenomenon in which, when an image with a high recording duty is recorded at high speed with an arrangement of minute discharge ports, the directions of inks discharged from the discharge ports located on an end are deflected toward the inside of the arrangement of the discharge ports. More specifically, referring to FIG. 18, the directions are deflected in a YR direction at an end of a head chip HC (n−1), while they are deflected in a YL direction at an end of a head chip HC (n) (“n” being an integer). This means that the landing points of discharged inks do not exactly match the positions of the corresponding discharge ports. Hence, when spliced heads are used, the white streaks are drawn in the recording material feeding direction in the recorded portions that correspond to the spliced portions of adjacent head chips.
Japanese Patent Laid-Open No. H5-57965 has disclosed the following method as a solution to the aforementioned problem.
Referring to FIG. 19, head chips are disposed such that at least two discharge ports of the same ink color overlap on a line in the recording material feeding direction in the spliced portions of the head chip HC (n−1) and the head chip HC (n), and data is decimated so that one of the overlapping discharge ports is selected to perform the recording of a line (the same luster) in the direction in which the recording material P is fed. This makes it possible to reduce to half the recording duty of each discharge port in the spliced portions at ends of the head chips, thus allowing deflection at ends to be controlled in the construction shown in FIG. 19.
However, another problem described below is posed if the construction shown in FIG. 19 in which the discharge ports of the same ink color in adjacent head chips are partly overlapped is actually used. It has been further discovered that the problem arises especially when the head constructed as illustrated in FIG. 19 is used to perform “one-pass” recording. One-pass recording is recording accomplished by one relative scan of an ink-jet head in the same recording area on a recording medium.
Referring now to FIG. 20, the recording material P is fed from a cyan discharge port row NAC of an ink-jet head or the head chip HC toward a black discharge port row NABk (X direction). At this time, since one-pass recording is carried out, ink droplets are shot onto the recording material P always in the order of cyan, magenta, yellow, and black in a non-spliced portion in which the discharge ports of the same color ink are not overlapped on a line in the recording material feeding direction (the X direction). Meanwhile, since the discharge ports of the same color ink are overlapped on the line in the recording material feeding direction in a spliced portion. Thus, although it depends on how data is decimated, a cyan ink dot, for example, is contaminated by an ink dot of another color adhering thereon or the cyan ink dot adheres onto a formed ink dot of another color.
In the case of the ink-jet recording, it has been known that even if ink droplets of two different colors are landed at the same point, the resulting dot undesirably exhibits two different colors to human eyes, depending on the landing order of the ink droplets. Hence, different landing orders result in different color shades between spliced portions and non-spliced portions, causing uneven color in the spliced portions.